Statistics How To

Non Parametric Data and Tests > Mood’s Median test What is Mood’s Median Test? Mood’s median test is used to compare the medians for two samples to find out if they are different. For example, you might want to compare the median number of positive calls to a hotline vs. the median number of negative … Read more

Design of Experiments > Consequential Validity What is Consequential Validity? Consequential validity refers to the positive or negative social consequences of a particular test. For example, the consequential validity of standardized tests include many positive attributes, including: improved student learning and motivation and ensuring that all students have access to equal classroom content. However, standardized … Read more

Statistics Definitions > Internal Consistency Reliability What is Internal Consistency Reliability? Internal consistency reliability is a way to gauge how well a test or survey is actually measuring what you want it to measure. A simple example: you want to find out how satisfied your customers are with the level of customer service they receive … Read more

Statistics Definitions > Kuder-Richardson Formula 20 (KR-20) What is the Kuder-Richardson 20? Kuder-Richardson Formula 20, or KR-20, is a measure reliability for a test with binary variables (i.e. answers that are right or wrong). Reliability refers to how consistent the results from the test are, or how well the test is actually measuring what you … Read more

Statistics Definitions > Contents: Stationarity Differencing 1. What is Stationarity? A time series has stationarity if a shift in time doesn’t cause a change in the shape of the distribution. Basic properties of the distribution like the mean , variance and covariance are constant over time. Types of Stationary Models can show different types of … Read more

Time Series > ARIMA modeling (sometimes called Box-Jenkins modeling), is an approach to modeling ARIMA processes—mathematical models used for forecasting. The approach uses previous time series data plus an error to forecast future values. More specifically, it combines a general autoregressive model AR(p) and general moving average model MA(q): AR(p)— uses previous values of the … Read more

Regression Analysis > Weighted Least Squares What is Weighted Least Squares? Weighted Least Squares is an extension of Ordinary Least Squares regression. Non-negative constants (weights) are attached to data points. It is used when any of the following are true: Your data violates the assumption of homoscedasticity. In simple terms this means that your dependent … Read more

Probability > Mutually Inclusive Mutually inclusive events have some overlap with each other. For example, the events “buying an alarm system” and “buying bucket seats” are mutually inclusive, as both events can happen at the same time. In other words, a car buyer can opt to buy and alarm and bucket seats. On a Venn … Read more

Regression Analysis > Prediction Interval What is a Prediction Interval? A prediction interval is a type of confidence interval (CI) used with predictions in regression analysis; it is a range of values that predicts the value of a new observation, based on your existing model. Prediction and confidence intervals are often confused with each other. … Read more

Statistics Definitions > Market Basket Analysis What is Market Basket Analysis? In market basket analysis (also called association analysis or frequent itemset mining), you analyze purchases that commonly happen together. For example, people who buy bread and peanut butter also buy jelly. Or people who buy shampoo might also buy conditioner. What relationships there are … Read more